DE2365457A1 - Lignin and cellulose recovery from oat husks - by digestion, methanol or acetone washing, concn and alkali chlorite or hydroxide treatment - Google Patents

Abstract

Lignin and cellulose are extd. from oat husks by (a) MeOH- or acetone- washing of the solid residue obtd. by digestion of oat husks in a 2-step process: (1) with alkali hydroxide or chlorite and (2) with inorganic acid, and concentrating the soln. to recover lignin, (b) treating solid residue from (a) with a dilute, alkali chlorite soln. having basic pH or at 88-95 degrees C with dilute alkali lye, opt. with addn. of H2O2. The thermoplastic, reactive lignin obtd. can be used as raw matl. for dyes and pesticides. Cellulose can be powdered and used, inter alia, as food, cellulose. Process allows complete utilisation of starting matl. In 1st step, AcOH is dissociated, crystallisation-inhibiting N-cpds. are dissolved, pentosans are not attackd. Cellulose is obtd. at water bath temps. in >70% yield.

Description

Patent attorneys

Dr. Ing.Walter Abitz _{20 # Septem} be.r 1974

Dr. Dieter F. Morf _{P 3} - _A

Dr. Hans-Α. Brauns 2365457

8 Munich 86, Pienzenaueratr. 28. £ OO 0 HO /

P 23 58 i * 72. 7- ¹ year TR.A.

SÜD-CHEMIE A.G. 8 Munich 2, Lenbachplatz 6

Process for the extraction of lignin and pulp from

Oat shells

D - (+) - xylose and its hydrogenation product, xylitol, are of considerable technical importance. Xylose can be used for various purposes in the food industry, for example, while xylitol has proven to be a very good sweetener for diabetics. Almost only hardwood species such as beech and chestnut are used as the starting material for the technical production of xylose. The yields are 10-12 % (cf., for example, * DT-PS 912 M40). A considerable disadvantage of this process is that the remaining wood substance, the so-called cellolignin, has not previously been able to be put to any useful technical use. /

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There is therefore a need for a process that once makes full use of the starting material allowed.

The invention relates to a process for obtaining lignin and cellulose from oat shells, which is characterized in that (a) the solid residue obtained by digesting oat shells in a first stage with alkali hydroxide or chlorite and in a second stage with mineral acid is available, washes with methanol or acetone and the solution is concentrated to obtain lignin, (b) the solid residue from stage (a) with dilute, a basic pH having alkali metal chlorite solution ^{or at about 88-95 0 C 'with dilute alkali} , optionally with the addition of hydrogen peroxide, treated.

The solid residue used according to the invention can can be obtained by a two-step digestion process, which is described below.

In the first stage, oat shells are opened with alkali hydroxide or chlorite, then in the second stage with mineral acid. This at least partially removes the hemicelluloses.

By using alkali hydroxide or chlorite in the first stage of the digestion process, the bound acetic acid present in the oat shells is split off. Also receiving the crystallization inhibitors nitrogenous substances and other impurities, whose nature nothing is yet known _s in solution, while the pentosan from the alkali metal hydroxide or -chlorit is not attacked. The acetic acid can be distilled off and ₉ if

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desired to be obtained from the distillate by extraction with a suitable solvent.

If alkali hydroxide is used in the first stage of the digestion process, sodium and potassium hydroxide, especially sodium hydroxide, are preferred. You can work in aqueous solution, for example. If you work at normal pressure, the concentration of the alkali hydroxide, based on solvent + alkali hydroxide, for example 0.6-4 wt. be. The preferred concentration range is 0.6-3, in particular 1-2% by weight. The temperature is 15-100 ^° C., preferably 25-60 ° C.

1.2% aqueous NaOH, for example, dissolves almost 20% at room temperature. the oat shell substance, the acetic acid is split off, the residue contains 50.5? Pentosan. 2% NaOH dissolves 38 % of ^{the oat shell substance at 50 °} C., the residue contains 46.6%. Pentosan, 3-strength NaOH dissolves 40 % ^{oat shell substance at 50 0} C, the residue contains 31? Pentosan and 4-? NaOH dissolved at 60 ⁰ C for about 45? Oat shell substance and the residue contains 30 pentosan.

If you work under pressure, you can, for example, with alkali hydroxide concentrations of 0.3 to 1.5 wt. work, preferably between 0.5 and 1.0 wt. The most favorable concentration is then 0.66% by weight. The pressure is preferably up to 3 atm and the temperature is preferably up to 125 C. The pressure is generally generated autogenously in the autoclave. When working under pressure with 0.66% NaOH, 25 - 27? disruptive substances dissolved and the residue contains 50 % pentosan.

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** "* ■ * 23654b?

If one digests in the first stage of the pulping process with Alkalichlorit _s so it is preferred also works with the potassium or sodium salt, especially the sodium salt. The concentration of the chlorite in the solvent, which is preferably water, is up to 10% by weight > 2 to 6% by weight are preferred . The pH of the reaction mixture is adjusted to be alkaline at the beginning, preferably to at least 11. In contrast to the usual reactions with alkali metal chlorite, this is not carried out with an acidic pH at the beginning. During the digestion, the pH goes down to around H - 5. It is carried out without pressure, the temperature is preferably between 15 and 60, in particular between 30 and 55 ^° C. The oat shells lose about 11 % of their weight, have a white-yellowish appearance, the acetic acid is split off and the pentosan content of the residue is increased to 49.8 % . Since only as much NaClO is consumed as corresponds to the acetic acid split off, the reaction solution can be reused a few times after replacing the used NaClOp, which must always be present in excess.

Those treated in the first stage of the digestion process After the acetic acid has been separated off by filtration, oat shells are diluted with a Mineral acid digested in a second stage at elevated temperature with or without pressure.

You can, for example, work with HpSO ₁ ,, HCl or HBr, for example in water, preferably with HpSO _1,. When working without pressure, it is preferable to use 1.5-6.0% by weight HCl or HBr or 1.5-6.0% by volume HpSO ^ and a ratio of liquid to solid of 3-6 Room sharing. The temperature is increased and is preferably 50-125 ° C, are then required about 2 to H hours for the second stage of the pulping process.

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When working under pressure, a pressure of up to 4 atmospheres, in particular 1-3 atmospheres, is preferably used, the temperature preferably being 125-135.degree. The acid concentration is preferably 0.2-0.6% by weight of HCl or HBr or 0.2-0.6% by volume HpSOjj and the ratio of liquid to solid should preferably be from k : 1 to 7: 1 volume / solid weight. The time required is approx. 1-2 hours.

After completion of the second process stage of the digestion process, the batch is filtered. The liquid can be processed into xylose or directly into xylitol. If you have worked with sulfuric acid in the second stage, you can neutralize with calcium oxide, calcium carbonate or preferably with barium carbonate in the calculated amount. After the precipitate has been separated off, a xylose solution is then obtained which can be immediately reduced to xylitol, whereas previously the solution had to be thickened or passed through an ion exchanger to remove acetic acid. The yield of pure xylose is up to 25 %; further xylose components, up to 10 %, can be isolated from the mother liquor.

Through this digestion process, the Bonds of the lignin with the polysaccharides are split without the lignin as in the known digestion process undergoes further polymerization.

The lignin can now easily be used in step (a) of the invention Process from the residue of filtration of the second stage of the digestion process by washing with methanol or acetone are then dissolved out as a yellowish-brownish powder, which is also obtained by various other solvents is resolved. The substance is thermoplastic and very reactive, it serves as a basic substance for technically useful products, such as dyes and pesticides. Further proportions of lignin can be dissolved in solution by pressure treatment with methanol to be brought.

Surprisingly, the residue remaining after the methanol treatment can already be used in step (b) at water bath temperature (approx. 88 C to 95 C) with dilute alkali, preferably

Are digested 4-iiger NaOH, to an almost white pulp, whereas otherwise a pressure boiling up to 180 ⁰ C is necessary - NaOH, for example at 1. The pulp is produced in a yield of approx. 70 % and can be obtained pure white by brief, conventional bleaching.

The residue can also be treated _{with alkali and H 2} O _{2 instead of with alkali.}

A third possibility of carrying out step (b) is to treat the residue with dilute alkali metal chlorite solution, in particular with sodium chlorite solution. In contrast to the known processes which work in the acidic area, an alkali metal chlorite solution which has been adjusted to a basic pH value, in particular to a pH value of at least 11, is used here. The residue is very easily broken down in this way, pure white, fine-fibred cellulose being obtained in a yield of approx. 85 % . This cellulose can be easily pulverized and can be used, among other things, as so-called food cellulose.

example 1

1 kg of oat shells are left to stand for 2k hours at room temperature with 4 l of 1.2 Sfiger NaOH solution with frequent shaking and working through, the decreasing titer of the solution being monitored. It is then filtered off with suction and washed well with HpO until the initially cloudy solution has become clear. A determination of the residue gives 50.5 % xylose (conversion of the pentosan content to the pentose). It is also now nitrogen-free.

The filtrate is acidified with sulfuric acid and the acetic acid is determined from the distillate; the oat shells have a content of 5.8 to 6 % acetic acid.

300 g (calculated on dry matter) of the residue are _{mixed with 1.2 l 3 vol .- # iger H 3} SO ₁₁ , whereby the liquid

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is completely absorbed. The mixture is then heated to 120-125 ° C. under reflux in an oil bath for 2 hours, the mass soon becomes mobile. After vacuuming and pressing well, it is washed with water, the piltrate is brown-yellow and separates when left to stand some sediment is deposited, therefore it is clarified with kieselguhr and decolorized with activated charcoal, whereby the solution retains a greenish-yellowish tinge, it is neutralized with the calculated amount of BaCO- and in a vacuum at 45 ° C concentrated to a light syrup. Crystallization occurs after inoculation and standing in the cold. The extracted crystals are briefly washed with 85% methanol. You get pure. Xylose in a yield of 75 »5 g. Further shares will be from the mother liquor by fractionation with methanol and isopropanol isolated in an amount of about 15 g.

The mother liquor remaining in this way is still a mixture of D-xylose, L-arabinose and glucose, which are difficult to separate.

As expected, the distillate no longer contains acetic acid.

In order to determine which amounts of xylose had passed into furfural during the hydrolysis process, a determination of the distillate is carried out with 2,4-dinitrophenylhydrazine; it shows that about 1.5 % of the xylose formed had further reacted to form furfural.

The hydrolysis residue is washed with methanol until it runs colorless and then has a weight of 160.1 g with 12.1 % pentosan, so that about 124 g of this substance have gone into the hydrolysis liquid. The brownish yellow methanol

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filtrate, which is HPO sustainably still moist from .Hydrolysenrückstand forth vrird eingeöunstet _t where the lignin after evaporation of the methanol, precipitates and is filtered off. The aqueous filtrate still contains residues of xylose and can be worked up.

For the purpose of extraction of pulp, 150 g of this residue with 20-5Og 80- # sodium chlorite dissolved in 1, ¹ J 1 H ₂ O, left to stand without acidification. After a while, the mass swells with discoloration. It is then stirred at approx. H0 ° C until the substance has turned light. It is then filtered off with suction and washed with HpO until the ClOp odor disappears and dried.

What remains is a pure white, flaky substance that is very easy to grind, with a yield of almost 90 %.

Another 100 g of the hydrolysis residue treated with methanol are treated with 700 ecm of 2-strength NaOH for 2 hours Heated water bath at approx. 95 ° C, sucked through a glass frit and washed with HpO until the first dark brown piltrate has become colorless. The residues of alkali are removed with acetic acid.

A fluffy, slightly brownish colored cellulose is also produced here, which becomes immediately white with a common bleaching agent. The yield is 70 % ₃ since the lye removes any pentosan components that are still present, which does not happen at the end of the process.

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B_g_i game 2

1 kg oat hulls are heated with 6 1 O, 66- $ NaOH (kO g) within iiO minutes at i25 ° C in O _S 9 to I ₅ 3 ATQ ,, then allowed to cool _s filtered off and washed well by means of non-woven fabric. The residue is approx. 750 g and contains 48.5% pentosan.

If the oat shells are only heated to 105 C in the autoclave under the same conditions _s
876 g with approx. 43 % pentosan.

105 C heated in the autoclave, results in a residue of

600 g of this residue are concentrated with * l 1 HpO and 2k ecm. H ₂ SO ₁ J heated in a stirred autoclave for 90 minutes to 13 ¹ I ⁰ C., It can be stirred well from 70 ° C. After filtration with suction, washing with H ₂ O and treating with methanol, the residue is 283 ₃ 7 g and has only 8.1% pentosan.

The acidic precipitate is neutralized with the calculated amount of BaCO, while stirring, and clarified with activated charcoal. After evaporation under reduced pressure at 45C to form a light syrup, approx. 25 % pure xylose crystals can be isolated, and a further 6 % can be obtained from the mother liquor.

100 g of the hydrolysis residue treated with methanol are stirred with 1 liter of 1.2% NaOH for 1 hour at 90/92 ° C. on a water bath and, after leaving to stand overnight, sucked through a glass frit. It is washed with hot water until the alkalinity has disappeared and the residue is dried. It consists of white cellulose with a methoxyl content of around 0.5 to 0.6 % . The yield is about 73 g.

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Claims (1)

P 23 58 472.? -4i - TR.A « m _% SÜD-CHEMIE A ₀ G ₀ P 3-A Claim A process for the recovery of lignin and cellulose from oat hulls j, characterized _s that (a) the solid residue ,, is obtainable by digestion of oat hulls in a first stage with alkali hydroxide or -chlorit and in a second stage with a mineral acid ₃ with methanol or acetone washes and the solution is concentrated to obtain lignin, (b) the solid residue from step (a) with dilute _s having a basic pH Treated or alkali chlorite solution at about 88-95 C with dilute alkali metal hydroxide solution _s optionally with the addition of hydrogen peroxide. 50982 271024 original inspected